JPH0617898A - Oil free type ball screw for semiconductor manufacturing equipment - Google Patents

Abstract

PURPOSE:To provide an oil free type ball screw for semiconductor manufacturing equipment with solid lubricating mechanism non-conductive with low dusting characteristics, high lubricating ability, high durability and high corrosion resistance. CONSTITUTION:A ball screw is provided with a screw shaft 1 with the spiral inner track face 1a formed at the outer peripheral surface, a ball nut 2 with the spiral outer track face 2a formed at the inner peripheral surface, plural balls 3 disposed at a spiral space formed between the inner and outer track faces 1a, 2a, and a ball circulating path. Diameter contractible C-shape seal rings 4 formed of ethylene tetrafluoride-ethylene perfluoroalkoxyde copolymer resin (PFA) with coil springs 7 mounted to the outer periphery are mounted to both ends of the ball nut 2 of the ball screw.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-lubricated ball screw used particularly in semiconductor manufacturing equipment.

[0002]

2. Description of the Related Art A ball screw has a plurality of balls arranged in a spiral ball circulation path formed between a screw shaft and a ball nut inserted through the screw shaft, and the screw shaft is circulated by rolling the balls. Power is transmitted between the ball and the ball nut, but the ball rolls with slip due to the combined force in the rotational and axial directions, so at the contact part between the ball and the ball circulation path. Rolling friction and sliding friction occur simultaneously. Further, when the balls collide with each other, the rotation directions of the adjacent balls are reversed, so that the relative sliding speed between the balls is double that of a single ball, and a large frictional force is generated. For these reasons, the selection of lubricant is particularly important for ball screws.

Usually, a fluid lubricant such as grease is used as a lubricant for the ball screw, but when it is used under a sealed vacuum that requires high cleanliness such as in semiconductor manufacturing equipment, the lubricant is used. Since the steam of is a pollution source of the environment, it is impossible to use a fluid lubricant such as grease. Therefore, under such an environment, the main part of the ball screw constituent member is generally covered with a solid lubricating coating. As a material for such a solid lubricating coating, layered materials such as molybdenum disulfide and soft metals such as gold, silver and lead are widely used.

[0004]

However, due to the rapid progress of technology in the field of semiconductor manufacturing in recent years, the line width of conductive patterns has become finer as the degree of integration of semiconductors has increased. There is a tendency to avoid particles from sticking to the top.

Unlike the fluid lubricant, the solid lubricant does not have a risk of contaminating the environment due to evaporation, but it is necessary to consider dust generation in the wear / transfer process of the lubricating coating.
For example, in a soft metal-based solid lubricant, the wear powder itself has conductivity, and therefore if the wear powder adheres to the conductive pattern, the conductive pattern may be short-circuited. Layered substance-based solid lubricants such as molybdenum disulfide are not electrically conductive, but have poor wear resistance and generate a large amount of dust.

Further, recent semiconductor manufacturing facilities are required not only to be used in a vacuum, but also to have functions such as dual use in the atmosphere and vacuum, corrosion resistance, and heat resistance. That is, the ball screw is mainly used in the semiconductor manufacturing equipment in the wafer processing process. The apparatus used in this step tends to be in-line for improving productivity, and a wafer transfer apparatus is required to have a ball screw which can be operated in both atmosphere and vacuum environment. Corrosion resistance and heat resistance are also required depending on the place of use.

In view of the above, the present invention solves the above problems and uses a solid lubrication mechanism of a ball screw, which has no grease or coated solid lubrication film and is apparently unlubricated, using a non-conductive material. It has characteristics such as low dust generation, high lubricity, high durability, and high corrosion resistance. Moreover, these characteristics are exhibited in both atmosphere and vacuum environment, making it suitable for semiconductor manufacturing equipment. The challenge is to use unlubricated ball screws.

[0008]

In order to solve the above problems, in the present invention, a screw shaft having a spiral inner raceway surface formed on the outer peripheral surface and a spiral outer raceway surface formed on the inner peripheral surface. A ball nut, a plurality of balls arranged in a spiral space formed between the inner and outer raceways, and a circulation member that connects the spiral spaces to form a series of ball circulation paths. The metal ball screw has a structure in which a seal ring made of a fluororesin is attached to both ends of the ball nut so as to be in close contact with the inner raceway surface and the gap between the ball nut and the screw shaft is sealed.

Further, the seal ring may have a diameter-reducing clearance formed by notching a part of the circumference in the radial direction, and an elastic member for reducing the clearance may be additionally provided.

[0010]

In the unlubricated ball screw for semiconductor manufacturing equipment according to the present invention, the seal ring made of fluororesin is in close contact with the inner raceway surface, and the fluororesin transfer film is continuously supplied little by little to this surface. Solid lubrication with a low coefficient of friction, which is peculiar to resin, is carried out with much higher durability (durability) than coating treatment. Such a fluororesin transfer film is sequentially supplied to the ball surface, the outer raceway surface, and the ball circulation path by the transfer, but even if the supply amount is small, the lubrication efficiency is good, and moreover, the film enters the minute irregularities. Therefore, the transition particles are less likely to scatter, that is, the dust generation is low. Further, since the seal ring seals the gap between the ball nut and the screw shaft, the particles do not scatter to the outside.

The seal ring gradually wears and the inner diameter expands due to use. However, since the seal ring has a diameter-reducing clearance and the elastic member reduces the diameter, the sealing function is deteriorated. To be prevented.

[0012]

The fluororesin used in the present invention can be used without particular limitation as long as it forms a lubricity transition film when it comes into sliding contact with a mating material, but as an example, polytetrafluoro Ethylene (PTFE), tetrafluoroethylene / perfluoroalkoxyethylene copolymer resin (PFA), fluorinated ethylene / propylene ether (EPE) or tetrafluoroethylene / hexafluoropropylene copolymer resin (FEP) (above, brackets The abbreviations and the like are preferred.

The above-mentioned fluororesin is molded into a ring shape by a method such as compression molding or extrusion molding. In order to improve wear resistance and creep resistance of the molded seal ring, a filler is used. May be added.

As such a filler, glass fiber,
Fiber materials such as carbon fiber, alumina fiber, zirconia fiber, aromatic polyamide fiber, potassium titanate whisker,
Silicon Carbide Whiskers, Graphite Whiskers,
Inorganic whiskers such as α-alumina whiskers, graphite, molybdenum disulfide, bronze, talc, mica, calcium carbonate, alumina, fluorinated graphite, calcium silicate, calcium phosphate, silica, aluminum hydroxide, potassium titanate, glass beads, carbon Examples include inorganic fillers such as beads.

Incidentally, to the extent that the effects of the present invention are not impaired,
It is also possible to blend a fluororesin with another thermoplastic resin to form a seal ring having desired physical properties.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment in which the present invention is applied to a guide plate type ball screw. This ball screw includes a screw shaft 1 having a spiral inner raceway surface 1a formed on an outer peripheral surface, a ball nut 2 having a spiral outer raceway surface 2a formed on an inner peripheral surface, and inner and outer raceway surfaces 1a and 2a. A plurality of balls 3 arranged in a spiral space formed between them and a circulation member (not shown) that connects the spiral spaces to form a series of ball circulation paths are provided at both ends of the ball nut 2. Is equipped with a seal ring 4 made of PFA.

As shown in FIG. 2, the seal ring 4 has an end face C having a peripheral groove 5 in the outer peripheral portion thereof and a diameter-reducing clearance 6 formed by notching a part of the peripheral portion with a constant width in the radial direction.
It is a character-shaped member. An annular coil spring 7 is attached to the circumferential groove 5 of the seal ring 4 in a stretched state, and is biased in a direction to reduce the clearance 6. The elastic member for reducing the diameter of the clearance 6 may be a known elastic member such as rubber other than the coil spring 7. Further, a female screw corresponding to the outer shape of the screw shaft 1 is formed on the inner peripheral surface of the seal ring 4 to form a contact surface 8.

The above-mentioned seal ring 4 is fitted and fixed in ring-shaped notches 9 formed concentrically with the shaft center on both end faces of the ball nut 2.

With respect to the obtained ball screw, the rotation speed is 40
0 rpm, preload amount of 15 kgf, vacuum degree of 10 ^-7 Torr level,
The ball screw was operated under the condition of room temperature to carry out a life test and a dusting test, and the results are shown in Table 1. The life time was evaluated by the time from the start of the test until it reached 5 times the initial torque.

Further, a ball screw of the second embodiment was manufactured in exactly the same manner as in the first embodiment except that the material of the seal ring 4 was PTFE, and the same life test and dust generation test as described above were conducted. The results are also shown in Table 1.

[0021]

[Table 1]

[Comparative Example] A ball screw assembled in exactly the same manner as in the first embodiment except that a silver lubricating coating is formed on the inner raceway surface 1a, the outer raceway surface 2a and the surface of the ball 3 by plating instead of the seal ring. A life test and a dusting test were performed under the same conditions as in the examples, and the results are also shown in Table 1.

As is clear from the results shown in Table 1, in Examples 1 and 2 of the present invention, the relative life was 1.4 as compared with the Comparative Example.
.About.2 times or more, and the relative dust generation amount is 7/10 to 1/10 or less, which shows extremely good durability and low dust generation property.

[0024]

As described above, the present invention is required in the semiconductor manufacturing field because the transfer film having a low coefficient of friction is supplied to the main part by the seal ring made of the fluororesin and the both ends of the ball nut are sealed. It has the characteristics of non-conductivity, low dust generation, high lubricity, high durability and high corrosion resistance, and is the most suitable as a seemingly unlubricated ball screw for semiconductor manufacturing equipment. Can be said.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment.

FIG. 2 is a perspective view showing the above seal ring.

[Explanation of symbols]

 1 screw shaft 1a inner raceway surface 2 ball nut 2a outer raceway surface 3 ball 4 seal ring 6 clearance 7 coil spring

Claims (2)

[Claims] 1. A screw shaft having a spiral inner raceway surface formed on an outer peripheral surface, a ball nut having a spiral outer raceway surface formed on an inner peripheral surface, and a spiral formed between the inner and outer raceway surfaces. In a metal ball screw having a plurality of balls arranged in a space and a series of ball circulation paths that connect the spiral space, a fluororesin seal ring is provided on the inner raceway surface at both ends of the ball nut. A non-lubricated ball screw for semiconductor manufacturing equipment, characterized in that it is closely attached and is installed so as to seal the gap between the ball nut and the screw shaft. 2. The seal ring has a diameter-reducing clearance in which a part of the circumference is cut out in the radial direction, and an elastic member for reducing the clearance is additionally provided.
Unlubricated ball screw for semiconductor manufacturing equipment described.